The male gamete and the female gamete are both specialised sex cells, but they differ greatly in their size and in their structure because they are adapted ...
Question 1 Report
The male gamete and the female gamete are both specialised sex cells, but they differ greatly in their size and in their structure because they are adapted for different roles. Fig. 4.1 shows a human egg cell, labelled G, and a human sperm cell, labelled H. The two cells have been drawn to the same scale so that their sizes can be compared directly with one another. The differences in their overall shape, their relative size and the structures they contain are clearly visible in the drawing. One of the two cells is able to move by itself, while the other is much larger and stores food that will be needed by the early embryo.
Use Fig. 4.1 and your knowledge of gametes and fertilisation to answer the following questions.
(a) Using Fig. 4.1, state two visible differences between cell G and cell H. [2]
(b) State which of these cells is the male gamete. [1]
(c) Explain how the sperm cell is adapted to reach the egg. [3]
(d) State what is meant by fertilisation. [2]
Answer Details
This question compares the two human gametes and tests the meaning of fertilisation. Cell G is the large egg; cell H is the small sperm with a tail.
(a) Two visible differences between G and H. [2] Any two of: cell G (the egg) is much larger than cell H (the sperm); cell H has a tail whereas cell G has none; cell G is rounded while cell H is elongated and streamlined. (1 each) These must be differences you can actually see in the drawing, not internal facts.
(b) Which is the male gamete. [1] Cell H, the sperm. (1)
(c) How the sperm is adapted to reach the egg. [3] The tail (flagellum) beats so the sperm can swim towards the egg (1); it contains many mitochondria that release energy from respiration to power this swimming (1); and the acrosome at its tip contains enzymes that digest the egg's outer coat and membrane so the sperm nucleus can enter (1). Each feature is matched to a job: move, power the movement, get inside.
(d) Meaning of fertilisation. [2] Fertilisation is the fusion of the nucleus of a male gamete with the nucleus of a female gamete (1) to form a zygote (1). The word "nuclei" is important, because it is the genetic material that joins.
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